The Geologic Time Scale

  • Humans subdivide time into useable units such as our calendar year, months, weeks, and days


  • Geologists also subdivide time- breaking it into useable, understandable segments
    • based on major geologic events
    • based on appearance (and disappearance) of significant life-forms
    • starts with formation of Earth’s crust followed by the appearance of ever-changing forms of life

Key Periods of Human History


  • We know that humans influence the biosphere - just by being humans
    • local vs regional vs global


  • On geologic times scales humans have existed in the Cenozoic era
    • our evolutionary trajectory takes us through the Pleistocene and Holocene
    • we are potentially in a new time period: Anthropocene


  • Understanding human impacts requires historical knowledge of each time period

Pleistocene Ice Age (1.8-0.1 mya)

  • Glaciers repeatedly advance from the Arctic over Europe and North America
    • ice up to a mile thick
    • temperatures ahead of the flow drop significantly.


  • Animal life evolved (or not) to handle temperature change
    • new species, range shifts, population declines


  • Hominid line continues to evolve during the Pleistocene
    • anatomically modern humans first appear during late stages


  • More than 200 genera of very large herbivores go extinct
    • 95% in North America
    • humans and climate

Holocene (12,000 -)




  • Begins after last glacial period, including glacial retreat
    • Earth experienced a warming trend


  • Climate change and megafauna extinction drive massive change in human behaviors


  • Rapid proliferation, growth and impacts of the human species worldwide

Holocene (12,000 -)


  • Begins after last glacial period, including glacial retreat
    • Earth experienced a warming trend


  • Climate change and megafauna extinction drive massive change in human behaviors


  • Rapid proliferation, growth and impacts of the human species worldwide


  • Significant advancements in technology and ‘urbanization’
    • resultant increases in human impacts

Neolithic period (12,000-6,000ya)


  • Set of developments that appeared in several places independently!


  • Development of agricultural crucial human landmark
    • plant cultivation and animals domestication
    • spread from several centers of origin


  • Origin of agriculture… necessity or opportunity?


  • Whether from migrating farmers or indigenous development, most continents were transformed

Neolithic period: Humans transitioned to permanent settlements

Neolithic period: Urbanization and Population growth

Neolithic period: Consequences of Urbanization

Industrial Age (1760 -)


  • Economic and social organization that began around 1760 in Great Britain
    • factors of production (trade, farming, natural resources) allowed it to happen


  • Replacement of hand tools with power-driven machines
    • power loom, steam engine, iron making


  • Concentration of industry in large establishments
    • fueled by coal mining
    • creation of ‘factories’

Industrial Revolution marks a major turning point in history



  • Every aspect of daily life was influenced in some way


  • Average income and population began to exhibit unprecedented sustained growth
    • creation of middle class


  • Represents the starting point for serious atmospheric change
    • based on fossil fuel emissions

Key Periods of Human History: The Anthropocene Epoch

  • New geologic era?
    • proposal submitted
    • would mark end of the Holocene


  • Many geologist criticize the idea
    • hard to define a period when you are in it
  • Interval of time where humans dominate key processes on Earth
    • anthropo, for “man,” and cene, for “new”

Does the Anthropocene begin in the Industrial Age?

Does the Anthropocene begin in the Industrial Age?

Does the Anthropocene begin in the Industrial Age?

The Great Acceleration: Post 1950


  • Dramatic, continuous surge in growth rate across a large range of measures of human activity


  • Socioeconomic parameters: population, economics, water usage, food production, transportation, technology


  • Earth system parameters: green house gases, surface temperature, and natural resource usage


  • Post-war revival age
    • fossil energy and new technology flooding the markets

What happended? Haber Bosch happened!


Exponential human growth puts pressures on Earth’s systems